Lubricant oils have been industrially used as gear oil, engine oil, lubricant oil for refrigerators, lubricant oil for fibers, lubricant oil for rolling, etc.
As the working conditions for various industrial machines become severe recently, industrial gear oil has come to be required to maintain their lubricating properties and detergency at high temperature. In particular, improved lubricating properties and detergency have come to be required for the industrial gear oil used in the process for baking food and thermosetting coating. There have heretofore been used lubricant oils of synthetic hydrocarbon type, carboxylic acid ester type or glycol type.
Synthetic hydrocarbon lubricant oil and carboxylic acid ester lubricant oil, however, are still insufficient in lubricating properties, and in addition they have such a drawback that they cannot be used as lubricant oil at high temperature because they form carbide when heated over a long period of time. On the other hand, though glycol lubricant oil is advantageous in that it does not form much carbide when heated over a long period of time, it has insufficient lubricating properties and high hygroscopicity. Accordingly, improvement thereof has been desired.
Engine oil has been required to have lubricating properties and dispersancy at higher temperature over a longer period to cope with improved performance of automotive engines. When addition of the additives for the engine oil is attempted to respond to such a requirement, it results in an increase in the addition amount thereof. The increase in the addition amount thereof induces harmful results such as precipitation or deposition of mayonnaise sludge.
Though there has heretofore been tried use of mineral oil in combination with synthetic hydrocarbon oil or carboxylic acid ester oil, the resultant base oil shows both insufficient lubricating properties and dispersancy when used at high temperature over a long period of time.
Lubricant oil for 2-cycle engines, different from that for the above-mentioned automobile engines, that is 4-cycle engines, is burnt after it is added to gasoline due to the mechanism of the engines, and therefore its detergency is especially important. Though castor oil, polybutene and the like have been used as lubricant oil for 2-cycle engines, both their lubricating properties and detergency are insufficient.
Gear oil for automobiles, especially for ATF is required to have a low friction coefficient and decreased change thereof with the lapse of time. Antifriction agents and friction-adjusting agents have therefore been used. Automotive gear oil containing these additives has a problem that the friction coefficient thereof increases with time.
With the alteration of a refrigerant gas for refrigerators to Freon R-134a (CH.sub.2 F--CF.sub.3) which is an ozone layer-nondestructive HFC, mineral oil and alkylbenzenes, which heretofore have been used for lubricant oil for refrigerators, have come not to be used therefor because it has no mutual solubility with the refrigerant gas. Glycol ether type lubricant oil has currently been developed for the lubricant oil for refrigerators where the above-mentioned refrigerant is used.
For example, U.S. Pat. No. 4,755,316 discloses a compression refrigerator composition composed of tetrafluoroethane and a polyoxyalkylene glycol having a molecular weight of 300 to 2,000 and a kinematic viscosity at 37.degree. C. of about 25 to 150 cSt. Such glycol ether lubricant oil, however, generally has insufficient thermal stability and high hygroscopicity, and it shrinks rubber sealing materials such as nitrile rubber (NBR) and increases their hardness.
As lubricant oil for fibers, carboxylic acid lubricant oil and glycol lubricant oil have usually been employed, but they cannot simultaneously satisfy lubricating properties and detergency.
Lubricant oil containing tallow as its main ingredient has been conventionally used as rolling lubricant oil. In spite of its high lubricating properties and sufficient rolling efficiency, such lubricant oil is extremely poor in detergency, and hence it requires a process for washing the remaining tallow. Though carboxylic acid ester lubricant oil has been used as rolling lubricant oil, it shows little practicality due to poor lubricating properties, despite its excellent detergency.
U.S. Pat. No. 3,627,810 discloses a process for preparing carbonates of higher alcohols, and the carbonates are described to be useful as hydraulic oil, lubricant oil and plasticizers.
U.S. Pat. No. 3,657,310 discloses a process for preparing carbonates represented by the formula ROCOO(AO).sub.n R'. These carbonates are monocarbonates having alkyl group at the molecular terminals and having a polyoxyalkylene group .in the molecular chain, and they are described to be useful as lubricant oil, hydraulic oil and plasticizers. In the above-mentioned formula, R and R' denote a monovalent aliphatic group, and A indicates an alkylene group having 2 to 4 carbon atoms, with n denoting an integer of not less than 1.
European Patent No. 089,709 discloses a process for preparing a carbonate of a higher alcohol by ester interchange reaction between a higher alcohol having a molecular weight of 100 to 270 and an alcohol carbonate having a low boiling point, and a lubricant oil composition containing such a carbonate of a higher alcohol.
Japanese Patent L-O-P No. 37,568/1973 discloses a motor transmitting liquid containing at least one carbonates represented by the general formula ##STR1## wherein R.sup.1 and R.sup.2 are each independently hydrogen, an aliphatic group, an aromatic-substituted aliphatic group, an aromatic group, an acyl group, an alkoxycarbonyl group or an aryloxy group, n is a number of 1 to 10, and X is an alkylene group having at least two carbon atoms in the main molecular carbon chain, the molecular chain optionally containing a cycloalkylene group, an aralkylene group, an arylene group or no less than one hetero atom. As examples of the above-mentioned carbonates, there have been proposed polyetheylene glycol polycarbonates having a polyoxyethylene group in the molecular chain and a hydroxyl group or an alkyl group at the molecular terminals. Such carbonates, however, have low mutual solubility with the above-mentioned hydrogenated fluorocarbon (HFC) which is nondestructive to the ozone layer, and therefore it is not appropriate to use them as lubricant oil for refrigerators. Moreover, these carbonates have such drawbacks that they have a high pour point, and that they have high hygroscopicity when they have hydroxyl group at their molecular terminals. Even in view of these drawbacks, these carbonates are not suitable for lubricant oil for refrigerators.
Japanese Patent L-O-P No. 3,865/1971 proposes a polyethylene glycol polycarbonate having a polyoxyethylene group in the molecular chain and a hydroxl group or an alkyl group at the molecular terminals. However, such a carbonate has, as described above, low mutual solubility with hydrogenated fluorocarbon (HFC) which is nondestructive to the ozone layer, and therefore it is not appropriate to use it as lubricant oil for refrigerators. Moreover, the carbonate has such drawbacks that it has a high pour point, and that it has high hygroscopicity when it has a hydroxyl group at its molecular terminals. Even in view of these drawbacks, the carbonate is not suitable for lubricant oil for refrigerators.
Japanese Patent L-O-P No.3,865/1971 also teaches that a polycarbonate may be obtained by allowing 1 or 2 mols of a diol to react with diphenyl carbonate to form 1 or 2 mols of a monoalcohol in a mixture of n mols of the diol and (n-1) mols of diphenyl carbonate. For example, said Japanese Patent L-O-P describes a process for preparing a polycarbonate having a decyl group at the molecular terminals, wherein said monoalcohol is n-decanol, said diol is polyethylene glycol, and the reaction is conducted by heating under a reduced pressure.
Furthermore, in the above-mentioned process, highly reactive diphenyl carbonate is preferably used as a starting carbonate. In addition, diphenyl carbonate is preferably used from the stand point of easy setting of the reaction conditions because of its high boiling point.
In contrast, when dimethyl carbonate or diethyl carbonate which is less reactive and has a low boiling point is used, it is not easy to terminate the molecular terminals substantially only with alkyl by the above-described method. Furthermore, the use of a catalyst is required when such a less reactive carbonate is used as a starting material, but removal of the catalyst having a high boiling point from the reaction products is not easy.
It is, however, industrially and economically very advantageous to use, as starting materials, dimethyl carbonate or diethyl carbonate which are less expensive than diphenyl carbonate.
It has already been known, in general, that a polycarbonate can be obtained by allowing a monoalcohol to react with a carbonate such as dimethyl carbonate.
However, by the prior art process for preparing polycarbonates wherein a polyol instead of a monoalcohol is allowed to react with the carbonate, the remaining unreacted carbonate is distilled off by heating after the reaction, and the catalyst is neutralized with acid, the desired polycarbonate cannot be obtained in a high yield.
The present invention is intended to solve the above-described problems involved in the prior art method, and an object of this invention is to provide lubricant oil compositions having excellent lubricating properties and detergency, and also having high mutual solubility with Freon which is nondestructive to the ozone layer. More in detail, a further object of this invention is to provide lubricant oil compositions capable of being especially suitably used as lubricant oil compositions for refrigerators in which an ozone layer-nondestructive Freon gas is used as a refrigerant.
A still further object of this invention is to provide a novel polyalkylene glycol polycarbonate having a polyoxypropylene group in the molecular chain and an alkyl group and an alkyloxyalkylene group at the molecular terminals.
Another object of this invention is to provide a process for preparing a polyalkylene glycol polycarbonate having molecular terminals substantially composed of hydrocarbon group only and containing almost no remaining catalyst, wherein dimethyl carbonate or diethyl carbonate is employed as a starting material.
Still another object of this invention is to provide processes for preparing specific polyalkylene glycol polycarbonates in a high yield.